Renal cell carcinoma (RCC), the most common human kidney cancer, is frequently infiltrated with tumorassociated macrophages (TAM) that can promote malignant progression. Here, we show that TAMs isolated from human RCC produce substantial amounts of the proinflammatory chemokine CCL2 and immunosuppressive cytokine IL-10, in addition to enhanced eicosanoid production via an activated 15-lipoxygenase-2 (15-LOX2) pathway. TAMs isolated from RCC tumors had a high 15-LOX2 expression and secreted substantial amounts of 15(S)-hydroxyeicosatetraenoic acid, its major bioactive lipid product. Inhibition of lipoxygenase activity significantly reduced production of CCL2 and IL-10 by RCC TAMs. In addition, TAMs isolated from RCC were capable of inducing in T lymphocytes, the pivotal T regulatory cell transcription factor forkhead box P3 (FOXP3), and the inhibitory cytotoxic T-lymphocyte antigen 4 (CTLA-4) coreceptor. However, this TAMmediated induction of FOXP3 and CTLA-4 in T cells was independent of lipoxygenase and could not be reversed by inhibiting lipoxygenase activity. Collectively, our results show that TAMs, often present in RCCs, display enhanced 15-LOX2 activity that contributes to RCC-related inflammation, immunosuppression, and malignant progression. Furthermore, we show that TAMs mediate the development of immune tolerance through both 15-LOX2-dependent and 15-LOX2-independent pathways. We propose that manipulating LOX-dependent arachidonic acid metabolism in the tumor microenvironment could offer new strategies to block cancer-related inflammation and immune escape in patients with RCC. Cancer Res; 71(20); 6400-9. Ó2011 AACR.

Both cancer-related inflammation and tumor-induced immune suppression are associated with expansion of myeloid cell subsets including myeloid-derived suppressor cells. However, little known regarding characteristics of myeloid cells in patients with bladder cancer. In this study, we analyzed myeloid cells from peripheral blood (PBMC) and tumor tissue that were collected from patients with superficial noninvasive and invasive urothelial carcinomas. Our results demonstrate that PBMC from bladder cancer patients contain two major CD11b myeloid cell subsets: granulocyte-type CD15 high CD33 low cells and monocyte-type CD15 low CD33 high cells. The number of circulating granulocytic but not monocytic myeloid cells in cancer patients was markedly increased when compared to healthy individuals. Both myeloid cell subsets from cancer patients were highly activated and produced substantial amounts of proinflammatory chemokines/cytokines including CCL2, CCL3, CCL4, G-CSF, IL-8 and IL-6. Granulocytic myeloid cells were able to inhibit in vitro T cell proliferation through induction of CD4 1 Foxp3 1 T regulatory cells. Analysis of bladder cancer tissues revealed that tumors were infiltrated with monocyte-macrophage CD11b 1 HLA-DR 1 and granulocytic CD11b 1 CD15 1 HLA-DR -myeloid cells. Collectively, this study identifies myeloid cell subsets in patients with bladder cancer. We demonstrate that these highly activated inflammatory myeloid cells represent a source of multiple chemokines/cytokines and may contribute to inflammation and immune dysfunction in bladder cancer.

Recent studies suggest that tumor-infiltrated myeloid cells frequently up-regulate COX-2 expression and have enhanced PGE₂ metabolism. This may affect the maturation and immune function of tumor-infiltrated antigen-presenting cells. In vitro studies demonstrate that tumor-derived factors can skew GM-CSF-driven differentiation of T(h)1-oriented myeloid APCs into M2-oriented Ly6C(+)F4/80(+) MDSCs or Ly6C(-)F4/80(+) arginase-expressing macrophages. These changes enable myeloid cells to produce substantial amounts of IL-10, VEGF, and MIP-2. The tumor-mediated inhibition of APC differentiation was associated with the up-regulated expression of PGE₂-forming enzymes COX-2, mPGES1 in myeloid cells, and the simultaneous repression of PGE(2)-catabolizing enzyme 15-PGDH. The presence of tumor-derived factors also led to a reduced expression of PGT but promoted the up-regulation of MRP4, which works as a PGE₂ efflux receptor. Addition of COX-2 inhibitor to the BM cell cultures could prevent the tumor-induced skewing of myeloid cell differentiation, partially restoring cell phenotype and down-regulating the arginase expression in the myeloid APCs. Our study suggests that tumors impair the intracellular PGE(2) catabolism in myeloid cells through simultaneous stimulation of PGE(2)-forming enzymes and inhibition of PGE₂-degrading systems. This tumor-induced dichotomy drives the development of M2-oriented, arginase-expressing macrophages or the MDSC, which can be seen frequently among tumor-infiltrated myeloid cells.